The present invention relates to a process for producing alcohols or aldehydes by reacting monoolefins with carbon monoxide and hydrogen.
So far, the method, for producing saturated aliphatic aldehydes and saturated aliphatic alcohols both having one more carbon atom than monoolefins by reacting the monoolefins with carbon monoxide and hydrogen (oxo synthesis reaction), which is known as the oxo synthesis process, has been widely employed. The alcohols obtained by this reaction are useful as raw materials for plasticizers, intermediate materials for agricultural chemicals, medicines and food additives, etc.
It is known that a cobalt carbonyl catalyst is useful in the above method for producing alcohols. The method using a cobalt carbonyl catalyst has advantages in that the rate of reaction is high and the recovery of the catalyst is easy, but also has the defect that large quantities of by-products are formed because of the use of the cobalt carbonyl catalyst having a high acidity. In the early stage of the reaction, a saturated aliphatic aldehyde having one more carbon atom than a monoolefin as a starting material is formed as the main product from the monoolefin, and then a saturated aliphatic alcohol having one more carbon atom than said monoolefin is formed by hydrogenation. Further, said aldehyde reacts with said alcohol to form an acetal, which causes formation of acetal-derived by-products. The acetal is readily hydrolyzed to form an aldehyde and an alcohol in an acidic aqueous solution. However, an ether, an ether aldehyde and an ether alcohol are also formed from the acetal as by-products which can not be utilized to produce the alcohol or aldehyde. Therefore, the problem with this method is to inhibit the formation of acetal and acetal-derived by-products. Shown below is a flow chart of the formation of by-products in the above-described oxo synthesis reaction. 
(1) saturated aliphatic aldehyde having one more carbon atom than olefin as a starting material
(2) saturated aliphatic alcohol having one more carbon atom than olefin as a starting material
(3) acetal
(4) ether alcohol
(5) ether aldehyde
(6) ether
(In the formula, R1 and R2 represent alkyl, etc., wherein R2 is alkyl, etc. having two more carbon atoms than R1.)
As a solution to the above problem, Japanese Published Examined Patent Application No. 1930/87 discloses a process in which water is added to the reaction system to inhibit a side reaction from acetal in-the presence of a hydrocobalt tetracarbonyl catalyst. However, this process is not satisfactory for practical use because an aldehyde and an alcohol coexist in the reaction system for such a long time that an acetal and acetal-derived by-products are formed in large quantities.
Japanese Published Examined Patent Application No. 57414/83 describes a process in which monoolefin remaining unreacted after the oxo synthesis reaction is further subjected to reaction in a high pressure gas separator. However, this process is not satisfactory for practical use either, because a special apparatus, i.e. a high pressure gas separator is necessary, and also in respect of the selectivity of monoolefin for aldehyde or alcohol and the formation of by-products.
Further, U.K. Patent No. 702,204B discloses a process for producing an oxygen-containing compound in which an olefin is subjected to reaction with carbon monoxide and hydrogen in the presence of a cobalt catalyst, and unreacted monoolefin is separated from the obtained reaction mixture and then subjected to reaction with carbon monoxide and hydrogen in the presence of a cobalt catalyst. However, this process is not satisfactory for practical use either, in respect of the selectivity of monoolefin for aldehyde or alcohol and the formation of by-products.
An object of the present invention is to provide a process for producing alcohols or aldehydes by reacting monoolefins with carbon monoxide and hydrogen which is suitable for industrial production in respect of formation of by-products and selectivity of a starting material for the desired product.
The present invention relates to a process for producing an alcohol or an aldehyde in which a monoolefin is used as a starting material to produce a saturated aliphatic alcohol or saturated aliphatic aldehyde having one more carbon atom than the monoolefin, comprising the step of reacting the monoolefin with carbon monoxide and hydrogen in the presence of a cobalt carbonyl catalyst until the conversion of monoolefin reaches 50-90% (the first reaction step), the step of separating unreacted monoolefin from the reaction mixture obtained in the first reaction step (the step of separation of unreacted monoolefin) and the step of reacting the separated unreacted monoolefin with carbon monoxide and hydrogen in the presence of a cobalt carbonyl catalyst (the second reaction step), wherein at least one of the first reaction step and the second reaction step is carried out in the presence of water.